This invention relates to a multiple turbine-generator plant and particularly to a cross compound turbine-generator plant, which has first and second turbine-generator sections.
Preferred embodiments of the invention relate to cross-compound turbine-generator plants which comprise a first generator rotated by a high pressure turbine and a low pressure turbine, and a second generator rotated by an intermediate pressure turbine and a low pressure turbine. The inlet of the high pressure turbine is connected to a superheater while steam exhausted from the high pressure turbine is reheated and returned for use by the intermediate turbine of the second turbine-generator section by the respective low pressure turbines of the first and second turbine-generator sections. In practical embodiments of this type of cross-compound turbine-generator, it is required to rotate the first and second generators in a predetermined synchronized rotating speed ratio, such as 3,000 R.P.M. and 1,500 R.P.M. (2/1 ratio of rotational speeds). This speed synchronization is necessary in order that the two generators may be locked in step electrically prior to connecting to an electrical network being supplied.
In a starting operation of this type of cross-compound turbine, U.S. Pat. No. 2,902,831, suggests employing a bypass line which is connected from a steam generator to the second turbine section across the first turbine section, so that the speed synchronization of the first and second sections may be accomplished by controlling a starting valve provided along the bypass line. However, in the case where the bypass line is connected across the high pressure turbine of the first section, the pressure at the exit of the high pressure turbine cannot but become higher, because the exit of the high pressure turbine is connected to the inlet of the intermediate pressure turbine of the second section, where high pressure steam is introduced through the bypass line. If the pressure at the exit of the high pressure turbine becomes higher, the high pressure turbine is required to rotate in a highly pressurized atmosphere which causes excessive temperature rise in the turbine blades due to friction heat. Also, if the exit pressure of the high pressure turbine becomes a higher, the amount of work done in the high pressure turbine becomes smaller and the speed synchronization of the first and second sections cannot be accomplished.
An object of the present invention is to provide a method and apparatus of operating a cross-compound turbine-generator plant in which a speed synchronization of multi-turbine sections can be attained in an efficient and inexpensive manner without causing excessive heat rise in the turbine blades.
A further object of the invention is to provide a method and an apparatus for operating a cross compound turbine-generator plant, with a bypass line which conducts steam, from steam sources to a second turbine section across a first turbine section.
According to preferred embodiments of the present invention, a cross-compound steam turbine generator plant is provided which includes a first electric generator and a second electric generator for generating electrical current with a predetermined frequency. The first generator is driven by a high pressure turbine and a low pressure turbine, and the second generator is driven by an intermediate pressure turbine and a low pressure turbine. During starting operating conditions, high pressure steam is separately supplied to the high pressure turbine by a main supply line and to the intermediate pressure turbine by a bypass line, with the exhaust steam from the high pressure turbine being advantageously vented so that excessive friction heat may be removed from this exhaust steam. This arrangement advantageously prevents damage to the turbine units during starting conditions while accommodating synchronization of the two generators. Further, the reduction in pressure at the exit side of the high pressure turbine during starting conditions improves the operating efficiency.
According to a first preferred embodiment of the invention a portion of the exhaust from the high pressure turbine is vented by means of a controlled dumping valve located in a vent line extending from the high pressure turbine exhaust to a condenser of the first turbine-generator section. In this arrangement, the dumping valve is preferably controlled by a controller which also controls the supply of driving steam into the high pressure turbine and the supply of driving steam to the bypass line during starting conditions, whereby the controller can advantageously also synchronize the speeds of the two turbine-generator sections.
According to another preferred embodiment of the invention a portion of the exhaust from the high pressure turbine is vented by means of a controlled dumping valve located in a vent line extending from the high pressure turbine exhaust to the low pressure turbine of the first turbine-generator section, thereby aiding in driving said low pressure turbine during starting conditions. Alternative preferred embodiments vent a portion of the high pressure turbine exhaust to assist in driving the low pressure turbine of the second turbine-generator section.
The dumping valves of preferred embodiments of the present invention are also preferably controlled to vent a portion of the exhaust from the high pressure turbine during stopping operations.
These and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein: